key exchange algorithm with optional parties [closed]

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Closed 8 years ago.

I need to generate a secret key (or password) with agreement of multiple parties out of which some parties are optional.

For example, Mr. A, B, C & D are members who can do agreement and out of which atleast two agreements are required to generate the secret. However the secret should be same for all such key agreements.

I went through Diffie-Hellman algorithm but it requires all keys. Essentially what i am looking at is 1 private key and n public key type of key exchange algorithm.

Please suggest some algorithms to have this behavior.

Answer 1

All Public Key cryptosystems I know of uses a 1-1 key relationship. So it's not possible with the standard algorithms available.

What you are looking for is a Threshold Cryptosystem or something like Shamir's Secret Sharing.